1. Field of the Invention
The invention relates to a coating composition and the use thereof, particularly for the field of printing.
2. Description of the Prior Art
It is often necessary to temporarily or semipermanently protect the surface of an article from staining. For example, when applying a coating fluid such as paint, it is necessary to prevent staining of the back surface, to cover parts to which the coating fluid is not to be applied, or to prevent staining of the end portion of a backing roll. Such surface protection is particularly important in the field of printing, which is a type of imagewise coating process.
In various types of printing such as letterpress, lithography, intaglio, screen printing, and collotype, there have been serious problems in that the ink is undesirably applied to the non-image area of a printing plate during printing and, as a result, the resultant printing has staining or spreading of the image. For example, letterpress or flexography, there may occur a problem in that ink is applied to the non-image area of a printing plate. In the case of printing with the use of a metal mask as described in Japanese Unexamined Patent Publication (Kokai) No. 56-67985, printing ink flows onto the back surface of the mask (i.e., the surface to be brought into contact with an object to be printed) during the printing, producing an ink spread in the printing boundary and making the printing unclear. To solve such a problem, the non-image area of the printing plate or the back surface of the metal mask may be treated to make it ink-repellent or stain-resistant. Thus, demand has arisen for a treating agent capable of rendering such properties to the surface of the plate or mask.
Further, there has been desired a means for preventing the ink-receptive area of a printing plate from being applied with ink, i.e., a means for converting the image area of a printing plate into a non-image area, or in other words, a method of correcting the image of a printing plate. In the process for the preparation of a printing plate, an ink-receptive defect in the non-image area of the printing plate may be produced due to various causes such as defects in the mask film, damage by a film edge and the presence of dust. Therefore, a means for deleting and correcting the defect is necessary. Particularly, in a waterless planographic printing plate having an ink-repellent layer made of a silicone rubber layer, while many advantages can be obtained due to the fact that no dampening solution is necessary during printing, the silicone rubber layer may have a defect. Therefore, the correction of the defects is an important process. Further, it may become necessary to convert an image area into a non-image area by deleting the image. Such correction of the printing plate can be attained by treating the defect on the plate or the image area of the plate to render it ink-repellent.
For the purpose of preventing such staining, there has hitherto been known a method for forming a water-repellent and oil-repellent film of a fluoroplastic such as polytetrafluoroethylene or a silicone resin onto the surface of an article to be prevented from staining. However, high temperature treatment is generally necessary for the formation of such a resin film. For example, in the process for coating a silicone resin onto a surface of a metal mask for the preparation of a printed circuit as disclosed in Japanese Unexamined Patent Publication No. 56-67985, a reactive silicone oil, SH-1107 (Toray Silicone Co., Japan), is coated into the surface by a brush and then cured at 150.degree. C. for 10 to 15 minutes. Further, in the processes for converting a presensitized printing plate into a waterless planographic printing plate, as disclosed in Japanese Examined Patent Publication (Kokoku) Nos. 50-34970 and 50-35442, a silicone composition is coated onto the surface of the presensitized printing plate and then cured at 180.degree. C. for 5 minutes or at 200.degree. C. for 1.5 to 2 minutes. These resins have poor adhesion to a substrate and the adhesion becomes poorer as the curing conditions become milder. It has therefore been necessary to cure them at a relatively high temperature as mentioned above. Thus, a complicated operation has been necessitated, and a severe limitation has been placed on substrates to which such resins can be applied. Therefore, it has been desired to develop a means for producing a stain-resistant, strong coating under mild conditions.